[QUOTE=77Univega]--- Beware of two things:
1. Some of the older 27" rims are not hook-bead rims, they are straight-sided rims which cannot handle high pressure tires (over 95 psi)
QUOTE]

This is a good point, but the straight sided flange rims are pretty rare. I work on a lot of old 27" rims and the only straight walls I found were on a '70's vintage Schwinn Le Tour. Made in Japan. I blew a lot of tubes before I figured out that the problem was with the straight-walled flange on the rim.